...that is not exactly the way it is.
Originally Posted by xsperf
i had zimmerman on my older bmw, and i have brembos on this one, they are both great. and about the cracking, thtas if the holes are DRILLED, usually they are drilled if its like a 'made in Taiwan' deal where they are a knockoff, replica, but the real deal is not actually drilled, the holes are molded
Cross-drilled rotors are machined, drilled, and the holes are double chamfered (beveled edges to reduce wear on pads). The inner (lower) bevel will act as a wear indicator and once reached you should change out the rotors.
Rotors are cast & machined and only a very few rotors are made with "holes-in" (some Porsche and other exotic car rotors). They still must be drilled out and chamfered because the "hole-in" casting is really just a dimpled casting and each "hole" (dimple) does not go totally through the rotor.
There is no easy cost effective way to make holes totally through a casting other that drilling them out because of the vented area between the inside and outside and the vanes within. To attempt do so would most certainly be hugely labor intensive and cost prohibitive.